The present invention relates to the manufacture of circuit systems containing integrated-circuit devices and, more particularly, to a circuit and method of using, in a circuit system which is designed to operate with a first integrated-circuit device operating at a first supply voltage, a second integrated-circuit device having the same functional characteristics as the first device and comprising at least a portion operating at a second supply voltage.
It is known that, in the manufacture of integrated circuits, there is a tendency to reduce as far as possible the area of the substrate of semiconductor material, typically silicon, in which the integrated circuit is formed. The reduction in size is achieved by the use of more and more refined techniques and tooling which increase the precision of the photolithographic processes and improve control over diffusion.
In the manufacture of MOS digital integrated circuits, the development of the technology is evident basically as a reduction in the minimum channel length which can be achieved for the transistors both of the logic circuits and of the memory cells, and as a reduction in the depth of the diffused source and drain regions of the transistors. These dimensional reductions are advantageous not only because of the saving in area involved, but also because of some functional aspects such as lower energy consumption and faster speed of operation.
However, there are cases in which it is not possible to make use of these advantages. An example is a digital integrated circuit designed to perform a certain function as a component of a complex circuit system which is mounted, together with other components, on a printed circuit board. The supply voltage of the integrated circuit is set at the design stage at an optimal value which is determined by the minimum length of the channels of the transistors of the logic circuits. If the integrated circuit as a whole, or a portion thereof, is reproduced on a reduced scale with the use of more advanced manufacturing techniques, the optimal supply voltage is also reduced. For example, upon changing from 0.35 xcexcm technology, which requires a supply voltage of 3.3 Vxc2x110%, to 0.25 xcexcm technology, the supply voltage must be reduced to 2.5 Vxc2x110%. In order to use a new-generation integrated circuit in the circuit system which was designed for using the integrated circuit of the preceding generation, it is necessary to modify the printed circuit board, for example, by adding a voltage reducer thereto. This modification is necessary when the average life of the product which contains the circuit system is longer than that of the technology by which the integrated circuits used therein are produced. (Currently, the life of a technological generation is slightly less than one year.) It is therefore sometimes necessary to forego the advantages of technological progress and to keep obsolete production lines in operation to provide the supplies and the spare parts which are required by the manufacturers of the products, or to modify the circuit systems contained in these products in order to adapt them to equivalent new-generation integrated circuits. The first solution is disadvantageous for the manufacturer of the integrated-circuit devices and the second is disadvantageous for the manufacturer of the circuit systems; naturally, both of these solutions adversely affect the cost of the product.
The object of the present invention is to define a method and to provide a circuit system to enable integrated-circuit devices of different generations to be used in the same circuit system without modifications or adaptations.
According to one embodiment of the invention, a circuit system is provided, configured to accommodate an integrated circuit. First and second voltage supply terminals are provided, which supply a voltage level consistent with the voltage requirements of a first-generation integrated circuit. An additional terminal is provided, with a filter capacitor connected between the additional terminal and the second voltage supply terminal. In the event that a first generation integrated circuit is used, the first and second voltage supply terminals provide power for the integrated circuit, while a direct connection is made within the integrated circuit between the terminal pins that make contact with the first voltage supply terminal and the additional terminal.
In the event that a subsequent-generation integrated circuit is used, a voltage reducer circuit is integrated into the subsequent-generation integrated circuit, with an input of the voltage reducer circuit connected to the first voltage supply terminal, and an output of the voltage reducer circuit providing a reduced voltage to the integrated circuit, according to the requirements of the integrated circuit. The output of the voltage reducer circuit is also connected to the additional terminal, where the filter capacitor provides filtering for the reduced voltage.